Androgen-binding protein (ABP) is produced by the Sertoli cells of the testis and enters the epididymis (the site of sperm maturation) along with other testicular secretions. Since its discovery about 9 years ago, it has been thought that ABP probably performs some important role in the regulation of testicular function or in the regulation of the androgen-dependent epididymis. However, thus far, no clear physiological role for ABP has been demonstrated. The experiments outlined in this application are designed to investigate the distribution of ABP in the testis, epididymis and other compartments of the body; and to study the function and metabolic fate of ABP. These objectives will be accomplished using photoaffinity-labeled ABP and immunological techniques. Photoaffinity labeled ABP ((3H)ABP) is ABP to which 17Beta-hydroxy-4,6-androstadien-3-one (triangle6-testosterone) has been covalently attached. This probe can be used to examine the distribution of ABP even if it has undergone extensive metabolism. Immunological procedures (that is the use of antibodies and radioimmunoassay) will be used to localize and quantitate immunologically active ABP. A comparison of the distribution of total ABP, assessed using (3H)ABP, with the distribution of immunologically active ABP will provide information on the sites of ABP degradation and utilization. Passive immunization studies will be done with the antibodies to ABP. If neutralization of endogenous ABP results in discrete alterations in reproduction function (e.g., changes in epididymal morphology or sperm maturation), information on the function of ABP will be obtained. An understanding of the mechanisms by which ABP may be involved in epididymal function and sperm maturation is crucial for developing methods and agents for post-testicular regulation of male fertility. Such information may also lead to procedures for alleviating infertility problems that may arise from malfunction of the epididymis.